1. Field of the Invention
The present invention relates to a starter. More particularly, the present invention pertains to an improvement in an electric motor for generating rotational force in a starter used to start an engine of a vehicle.
2. Description of the Prior Art
A conventional starter used to start an engine of a vehicle has heretofore been arranged in the manner shown in FIG. 6.
The conventional starter 1 shown in FIG. 6, comprises a dc motor 2, an overruning clutch 4 slidably fitted on an output rotary shaft 3, an epicyclic reduction gear 5 which transmits the rotational force from an armature rotary shaft 2a of the dc motor 2 to a clutch outer member 4a of the overrunning clutch 4 through the output rotary shaft 3 after reducing the speed thereof, and a shift lever 8 having one end thereof engaged with the plunger rod of an electromagnetic switch 6 disposed at one side of the dc motor 2 and the other end thereof engaged with an annular member 7 secured to the overrunning clutch 4 in order to cause the overrunning clutch 4 to slide on the output rotary shaft 3.
In the conventional starter 1 of the type described above, a commutator 2b of the dc motor 2 consists of segments 2c circumferentially spaced at equal intervals to define with their peripheral surfaces a brush slide contact surface, and a resin portion for insulation which is provided between the segments 2c. More specifically, a tubular member 2d which has an insert 2e for use in a press-fitting buried in the inner peripheral surface and which has a multiplicity of segments 2c buried in the outer peripheral surface is formed of a resin material by integral molding process. Each segment 2c of the commutator 2b is connected at a riser portion 2h thereof to a lead wire of an armature coil 2g wound on an armature core 2f. A brush means 9 is disposed around the outer periphery of the commutator 2b. The brush means 9 includes a brush holder 9b which retains brushes 9a. Each brush 9a is biased radially inward of the commutator 2b from the outer side thereof by a spring 9c so as to be pressed against the brush slide contact surface defined by the peripheral surface of the commutator 2b.
Since in the conventional starter 1 the brushes 9a are pressed against the peripheral surface of the commutator 2b by the springs 9c, the process of assembly necessitates a step in which the springs 9c are expanded outward and, while this is being done, the brushes 9a are attached to the holder 9b. Accordingly, it is preferable to ensure that a space is left around the commutator 2b when assembling the brush means 9 with a view to facilitating the assembly. For this reason, the machine frame of the dc motor 2 is composed of a yoke 2i which surrounds the armature core 2f and a rear bracket 2j which is provided as a separate member to close the rear end of the yoke 2i. The rear bracket 2j is attached to the open end of the yoke 2i so as to close it after the brush means 9 has been mounted on the commutator 2b. The rear bracket 2j is then secured rigidly to a front bracket 11 by means of through bolts 10, and the brush holder 9b is secured rigidly to the bracket 2j by means of screws 12.
Accordingly, the conventional starter 1 needs an exceedingly large number of parts and has a complicated arrangement, and it therefore suffers from the problem that assembly is considerably complex and troublesome task.